Claude Code used to have a warning that toggling thinking within a conversation would decrease performance: > Changing thinking mode mid-conversation will incr

Claude Code used to have a warning that toggling thinking within a conversation would decrease performance: > Changing thinking mode mid-conversation will increase latency and may reduce quality. For best results, set this at the start of a session. Neither OpenAI nor Anthropic exposes raw thinking tokens anymore. Claude Code redacts thinking by default (you can opt in to get Haiku-produced summaries at best), and OpenAI returns encrypted reasoning items. Either way, first-party CLIs hold opaque thinking blobs that can't be manipulated or ported between providers without dropping them. So cross-agent resume carries an inherent performance penalty: you keep the (visible) transcript but lose the reasoning.